The objective of this project is to provide an independent surveillance of the health status of rats maintained in contractor facilities for the nine-year rat colonies. The Project Officer will select animals to be shipped from the NIA colony/colonies to an independent laboratory (Microbiological Associates, Inc.) for health and pathology evaluation from the inventory maintained in the NIA Resource Development office which effectively samples the range of ages and holding rooms that characterize the colony/colonies. The evaluation to be performed will include: -Gross Pathology: observation of organs and tissues for gross pathological lesions; -Histpathology: Lung, liver, kidney, spleen, brain, any abnormal tissue from gross pathology; -Microbiology: mycoplasma, salmonella, psuedomonas, any abnormal discharges, exudates or inflammatory process; Parasitology: endoparasites, ectoparasites; and Serology: rat viruses.